The analysis is just beginning of a 7-generation population of house mice (Mus musculus) that lived in an environment that was optimum for 200 adults. Population growth was regulated so that over eight successive 200 day periods the adult population formed a series of 16, 100, 200, 400, 800, 1600, 1600, 374 individuals. At optimum density, approximately 12 adults lived in each of the 16 similarly constructed areas (termed cells), of the habitat. During the 6th period only sufficient pups of the 7th generation survived to maintain the population at eight times optimum density. Only 2 pups survived to form the 8th generation. No pups survived during the 8th period when the population was reduced to 372 7th generation adults. We had anticipated that living at 4x optimum density would precipitate population extinction despite our efforts to maximize favorability of habitat conditions. Our long-range objective was to understand the process of dissolution of organization of biobehavioral systems existing in a constant environment. Places to which each mouse customarily retires define its core residential range. Local groups are comprised of individuals with overlapping core ranges. Each habitat cell contained 70 structurally unique numbered subspaces. Each of the 2,500 mice was captured resting many times during its average 550 day life span. After random dispersal as juveniles, a period of core range stability usually ensues. Location of core range may shift 2 or more times during adulthood with intervening range instability. Algorithms and computer programs have been completed to define core range stability and instability and thus the periods of heightened stability of the entire population. Such analyses of resting-time residence are intended to provide a logical structure for analyzing our extensive data base of behavior observations.